.w {
    //版心宽度 1200px
    margin: 0 auto;
    width: 1200px;
}
a {
    text-decoration: none;
    color: black;
}
li {
    list-style-type: none;
}
.flex-row {
    display: flex;
    flex-direction: row;
}
.flex-column {
    display: flex;
    flex-direction: column;
}
